Network Working Group O. Lendl
Request for Comments: 5105 enum.at
Category: Standards Track December 2007
ENUM Validation Token Format Definition
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
An ENUM domain name is tightly coupled with the underlying E.164
number. The process of verifying whether the Registrant of an ENUM
domain name is identical to the Assignee of the corresponding E.164
number is commonly called "validation". This document describes a
signed XML data format -- the Validation Token -- with which
Validation Entities can convey successful completion of a validation
procedure in a secure fashion.
Table of Contents
1. Introduction ....................................................2
2. Data Requirements ...............................................2
3. Digital Signature ...............................................3
4. Field Descriptions ..............................................4
4.1. The Element ...................................4
4.2. The Element ....................................5
5. Examples ........................................................6
5.1. Unsigned Token without Registrant Information ..............6
5.2. Signed Token ...............................................6
6. Formal Syntax ...................................................8
6.1. Token Core Schema ..........................................9
6.2. Token Data Schema .........................................10
7. Other Applications of the Token Concept ........................12
8. IANA Considerations ............................................12
9. Security Considerations ........................................13
10. Acknowledgements ..............................................14
11. References ....................................................14
11.1. Normative References .....................................14
11.2. Informative References ...................................15
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RFC 5105 ENUM Validation Token December 2007
1. Introduction
In the case where an ENUM (E.164 Number Mapping [1]) domain name
corresponds to an existing E.164 number [2], the delegation of this
domain needs to be authorized by the Assignee of the corresponding
E.164 number. In the role model described in [15], the entity that
performs this check is called the Validation Entity (VE).
By conveying an ENUM Validation Token -- a signed XML document -- to
the Registry, a VE certifies that delegation requirements have been
met and are current.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [3].
2. Data Requirements
In this model, the Token is the only piece of data passed from the VE
to the Registry. Therefore, the Token needs to contain at least as
much information as the Registry requires to grant the delegation of
the requested ENUM domain according to its registration policy. As
such, the Registry will need confirmation that:
o the Token was created by an accredited VE,
o the Token's duration of validity conforms to the policy,
o the validation procedure employed has met minimum requirements as
set forth by policy,
o and that the Token is protected against tampering and replay
attacks.
Beyond such mandatory information, the Token may optionally include
number holder information, in particular, to simplify future
revalidations.
For example, if initial validation requires the steps "Check the
identity of the Registrant" and "Check the ownership of an E.164
number", then a later revalidation only needs to re-check the
ownership as the identity of the Registrant does not change.
As the Token will be included (see e.g., [16]) in XML-based Registry/
Registrar protocols like the Extensible Provisioning Protocol (EPP)
[13], it is a natural choice to use XML to encode Validation Tokens.
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RFC 5105 ENUM Validation Token December 2007
3. Digital Signature
According to the architecture model the propriety of an ENUM
delegation depends on the trust relationship between the Registry and
the VE. In general, an untrusted link between the Registry and VE
should be assumed (for instance, the Token is passed along with the
registration request by a Registrar, who might have no role in
asserting the right-to-use). Therefore, the Token must be protected
against forgery, tampering, and replay-attacks.
A digital signature on the token:
o asserts that the token was indeed generated by the indicated VE
(authenticity).
o guarantees that the token was not tampered with in transit
(integrity).
o enables auditing the validation process (non-repudiation).
The cryptographic signature on the token follows RFC 3275 (XML-DSIG
[4]). As tokens might be transmitted as part of an already XML based
protocol, the exclusive XML canonicalization [9] MUST be used. This
transform guarantees that namespace declarations inherited from the
surrounding XML do not invalidate the signature. In order to make
the signature an integral part of the token, the
"enveloped"-signature mode is employed. The signature covers all
information contained in the Token.
XML-DSIG offers a number of cryptographic algorithms for digesting
and signing documents and recommends SHA1/RSA-SHA1. Recent advances
in cryptanalysis have cast doubt on the security of SHA1, thus
rendering this recommendation obsolete (see e.g., the Security
Considerations of [14]). RFC 4051 [5] defines how additional
algorithms can be used with XML-DSIG.
Validation Entities MUST be able to sign tokens according to
XML-DSIG, MUST support RSA-SHA1 and RSA-SHA256 [5], MUST support RSA
key sizes of 1024 and 2048 bits, and MUST be able to embed X.509 [10]
certificates. The Registry MUST define which signature algorithms
and key sizes it will accept in Validation Tokens as part of its
local policy.
The choice of a RSA-based signature does not require a public key
infrastructure. Whether the Registry acts as a certification
authority, accepts certs from a public certification authority, or
only accepts pre-registered keys is a local policy choice.
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RFC 5105 ENUM Validation Token December 2007
4. Field Descriptions
The Validation Token is structured into three parts: the basic
validation information, additional information about the Registrant,
and the digital signature. The XML schema can be found in Section 6.
4.1. The Element
A token MUST contain a element that contains the
following:
o A single validation "serial" attribute identifying a validation
token for a certain VE. It must be unique per VE.
o A single element containing the underlying E.164
number in fully qualified (international) format.
o An optional element. If present, it indicates
that the whole number block starting with up to and
including has been validated. To avoid
ambiguity, both numbers MUST be of the same length.
o A single element identifying the VE.
o A single element identifying the Registrar on whose
behalf the validation was performed.
o A single element identifying the method used by the VE
for validation.
o A single attribute containing the date of
validation formatted as "full-date" according to RFC 3339 [6].
o An optional attribute marking the expiration date
of the validation token formatted as "full-date" according to RFC
3339. The Registry will automatically revoke the delegation at
this date unless a new Token has been submitted that extends the
lifetime of the validation. A missing indicates
infinite validity of the Token.
The format and the uniqueness-constraints of these IDs is left to the
local policy of the Registry.
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RFC 5105 ENUM Validation Token December 2007
4.2. The Element
A token may contain a section containing information
about the number holder, consisting of the following elements:
o A single element containing the full name of the
organization to which the Registrant is affiliated.
o A single element. If the Registrant is
a company, then this field can be used to uniquely identify this
company by its official registration number within the local
country. The interpretation of this field is thus
country-specific.
o A single element.
o A single element.
o A single element.
o A single section containing the following elements:
* A single optional
* A single optional
* A single optional
* A single optional
* A single optional
* A single optional
o Up to 10 elements containing full E.164 numbers.
o Up to 10 elements containing full E.164 numbers.
o Up to 10 elements.
All elements directly under are optional. The
element specifies the country using the alpha-2
country code from ISO 3166-1:2006 [11] (including updates published
by the 3166 Maintenance Agency). The definition of the first five
elements within the element conforms to the second version
of the E.115 Computerized Directory Assistance [17].
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RFC 5105 ENUM Validation Token December 2007
5. Examples
5.1. Unsigned Token without Registrant Information
This basic Token without any information about the Registrant and
without the cryptographic signature shows the basic layout of the
Token.
+442079460200+442079460499ACME-VEreg-4711422007-05-082007-11-01
5.2. Signed Token
This example uses an X.509 based signature that includes the
certificate of the signing validation entity. Thus, the validity of
the signature can be verified without the need for a key-server. A
valid signature is a necessary, but not sufficient, condition for a
valid Token. Any entity evaluating a Token needs to check other
factors as well, e.g., the certificate and the XML schema.
+442079460123ACME-VEreg-4711422007-05-08
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RFC 5105 ENUM Validation Token December 2007
Example Inc.4711Dr.MaxMustermannMain101010LondonLondonGB+442079460123mm@example.comVxqsBxSNPFwPAUlCHts3g3DehcexnB1dqUz+GypLZ0k=
QKqphKRNPokVZFbenje+HZZV+RLrNweGnlWBw7ngAtH+rtuslR8LhMLmC4DlBb9V
HvKItl+7zLGm3VgYsqfHH8q3jCl1mFxUIuLlIPqtpJs+xAHAJDzZ+vmsF/q2IgrS
K0uMmKuU5V1gydDBOvIipcJx+PrPYyXYZSjQXkWknK8=
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RFC 5105 ENUM Validation Token December 2007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6. Formal Syntax
The formal syntax of the validation token is specified using XML
schema notation [7] [8]. Two schemas are defined: The "token core
schema" contains mandatory attribute definitions, and the "token data
schema" defines the format of the optional "tokendata" section. The
BEGIN and END tags are not part of the schema; they are used to note
the beginning and ending of the schema for URI registration purposes.
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RFC 5105 ENUM Validation Token December 2007
6.1. Token Core Schema
BEGIN
Validation Token core schema